This invention is generally in the field of methods and devices for sealing parts together, and more particularly hermetic sealing methods for devices and/or implantable medical devices.
In many applications, there is a need to join, bond, or otherwise seal two or more parts together. Oftentimes, particularly with medical implant devices, these seals must be biocompatible and hermetic, for example, to protect the purity or quality of the reservoir contents.
Examples of devices that may require sealing are described in U.S. Pat. Nos. 5,797,898, 6,527,762, 6,491,666, and 6,551,838, which are incorporated by reference herein. These devices for the controlled release or exposure of reservoir contents include a plurality of reservoirs in which the reservoir contents are contained. The reservoirs may contain pharmaceutical formulations for release, sensors for exposure, or combinations thereof. In constructing these devices, it often is necessary to seal two or more substrates or other parts, which may contain the reservoirs and reservoir contents or electronic components associated with operation of the device.
Various sealing approaches are known in the art. Examples include those described in U.S. Pat. No. 6,730,072 (describing the use of a polymeric gasket and backplate) and U.S. Pat. No. 6,827,250 (describing various techniques for hermetically sealing micro-reservoirs, including high temperature laser or resistive welding, soldering, ultrasonic welding, and metal compression gaskets), and in U.S. Patent Application Publication No. 2005/0050859 A1, which are incorporated by reference herein. These methods may not be suitable or ideal for all sealing applications.
Under ambient conditions, metal surfaces will not typically bond when brought together because the metal surfaces are covered with a surface oxide, an organic contaminant, or both, which act as barriers to metal bond formation. However, the compression of two flat metal surfaces at pressures beyond the yield stress of the metals can cause the surfaces to deform, displacing the barriers and exposing clean metal which can bond. Yet, even with significant metal deformation of two flat surfaces compressed together, the actual bonding area is significantly lower than the mating surfaces area. (Mohamed & Washburn, Welding Research Supplement, September 1975, pp. 302s-310s; Welding & Joining Processes 3.371J/13.391J Fabrication Technology, T. Eagar, MIT) This low bonding area characteristic is due to two phenomena. First, the surface fraction of newly exposed metal is not a strong function of the amount of deformation for flat surfaces. Second, asperities prevent the majority of the surface from interacting and bonding. Because the surfaces are not completely bonded, leak paths may be present, preventing a hermetic seal from forming.
Ferguson, et. al., “Contact Adhesion of Thin Gold Films on Elastomeric Supports: Cold Welding Under Ambient Conditions,” Science, New Series, 253(5021): 776-78 (Aug. 16, 1991) discloses a gold-to-gold bond under ambient conditions by contacting thin gold metal surfaces on top of compliant polymers. However, the result is a bonded interface with “islands” of contaminants that are not bonded. These islands could form a contiguous leak path.
It would be desirable to provide improved sealing methods, for forming hermetic seals at low temperatures with a range of materials. It also would be desirable to individually, hermetically seal a plurality of closely spaced reservoirs between at least two substrates, in a process that is relatively simple and cost effective, particularly for large scale production with high reliability.